Method

Description

Force methods

Surface and interfacial tensions are called “static” and “quasi-static” when their values, under constant external conditions, do not change, stop changing, or change very slowly. They are therefore in or very close to thermodynamic equilibrium. To determine this, a ring (Du Noüy method) or a plate (Wilhelmy method) is placed in contact with the surface of the liquid and the resulting force is measured. This force is a measure of the surface/interfacial tension. The geometry of the measuring body is set by standards, e.g. ATM D971 and DIN 53914.

The Du Noüy method is preferred over the plate method despite greater effort (correction of measured value), as it gives triple the resolution. Another reason is simpler cleaning of the more robust measuring body, as well as the lower resolution. The ring method offers particular advantages in fully automated measurements, such as the automatic determination of concentration dependencies (CMC) and in quality control.

Method

Description

The perfect symbiosis between proven theory and modern technology

The big brother of the LAUDA TD 1 is a highly precise “allround” measurement device for all types of interfaces. Thanks to the high level of automation it is also suitable for use in quality control. It is essential for interfacial researchers due to its high precision and numerous measuring options. The combination of a fast, microgram accurate force measuring system with the high resolution distance encoder is the basis for the wide application range of the LAUDA tensiometer TE 3.

Robust and with legendary reliability, the LAUDA Tensiometer TE 3 measures with high precision. It is extremely simple to operate and can withstand unfavourable ambient conditions and aggressive vapours and chemicals. The large open interior simplifies the insertion of samples. A detachable housing provides additional protection. The double spindle guide in combination with a PLL controlled DC motor provides virtually clearance-free and frictionless, and thus vibrationless table movement over a wide speed range.

Method

Description

Worldwide the only device that operates on the Fainerman Method

In the MPT 2, the pressure is not measured inside the bubble as is customary in other devices, but in a buffer volume before the capillary. There, the pressure always corresponds to the maximum bubble pressure from which, using the known internal radius of the capillary, the surface tension can be derived.

An integrated pump produces a gas flow that is held constant at the respective specified value. For measurement, a gas, usually air, is introduced into the sample through a very narrow capillary. Depending on the gas flow rate, either a jet or individual bubbles are produced.

In the jet range, the gas flow is proportional to the pressure drop along the capillary. At a certain point, the jet will split up into individual bubbles. The pressure now serves to inflate the bubble and, according to LaPlace, depends from this point forward on the surface tension and bubble radius. The MPT 2 is the only instrument based on the Fainerman method and allows surface tensions to be determined precisely at previously unavailable surface ages of less than one millisecond!